update license headers

src/ahriman/models/property.py

@@ -1,3 +1,7 @@
+#
+# Copyright (c) 2021 ahriman team.
+#
+# This file is part of ahriman
 # (see https://github.com/arcan1s/ahriman).
 #
 # This program is free software: you can redistribute it and/or modify